MANAGEMENT

Refracturing: Technology and Reservoir

Understanding are Giving New Life to Depleted Unconventional Assets Sherif Foda, Production Group President, Schlumberger

The unconventional boom that has ventional resource development to the rienced improved production from both swept across North America over the next level: refracturing. While refractur- the infill and depleted wells. past decade is a testament to how game- ing of the Barnett Shale generated inter- In 2014, Schlumberger assembled a changing technology combined with est in 2008–2009, the development of team of experienced geoscientists from expanded knowledge and understand- new diversion technologies is enabling the hydraulic fracturing and reservoir ing has transformed the paradigm of oil and gas operators to once again con- subsurface disciplines to determine the hydrocarbon production. Ongoing devel- sider refracturing as an economic alter- criteria for developing a workflow to opment of horizontal drilling and com- native to drilling new wells. diagnose potential well candidates for pletion technologies and sophisticated While producers are still work- refracturing. The team formed a con- downhole logging tools have been instru- ing to understand the mechanisms of sortium with several of the most active mental in increasing efficiency to make unconventional production and how operators in the oil- and liquids-rich oil and gas shale plays economically via- wells behave and flow, they do have a Eagle Ford Shale. Members of the con- ble. Today, more than 70,000 horizontal much better understanding of the sub- sortium are providing the necessary data wells are producing from unconventional surface than they did in the early days to define wells, most of them 1 to 4 years resource plays with massive, multistage of a play as more wells have been drilled old, which would be good refracturing fracturing campaigns. and data collected from these wells are candidates in the play. By joining forc- Over the years, however, operators pieced together. At the same time, frac- es in this unique study, the consortium have learned that reservoir heterogene- ture models for determining optimum members are creating a critical mass of ity and low-permeability rock present treatment designs and technologies that data, with the results of the well studies challenges that can limit the potential can divert treatments to new unstimu- shared among the companies. This has of unconventional development. Despite lated rock are now available and proven. facilitated accelerated learnings and best the fast pace of technological advances, This enhanced reservoir under- practices in well candidate selection and production log analyses reveal that con- standing and access to technology are refracturing design. ventional completion designs, including incentivizing operators to take a second The overriding objective of the proj- the practice of placing perforation clus- look at refracturing as a feasible and ect is to gain back more than 60% of the ters evenly along the lateral, may not cost-effective alternative to drilling new IP while spending significantly less than be the best approach to production in wells. By reinvigorating existing, often 40% of the IP costs. To achieve this, the these plays. Production logs show that depleted, assets, companies can enhance refracture treatment must be moved out on average, 40% of the perforation clus- hydrocarbon recovery while boosting of the existing fracture network and into ters in a given lateral are not contributing cash flows. new, unstimulated rock while preventing to production. the refracturing process from interfering Unconventional wells also exhibit A Unique Consortium with offset wells. Early results from opti- rapid declines from initial production Refracturing also provides the added mized refracturing treatments on candi- (IP) rates, sometimes by as much as 60% benefit of protecting the depleted wells date wells have shown that the process to 80% during the first year of opera- from the negative effects associated with can provide a timely boost in cash flow tion. If early IP rates are not managed, fracture hits when drilling offset wells. from existing well inventories by enhanc- or choked, properly, subsequent steep Companies historically have encountered ing recovery of hydrocarbons. declines can cause long-term damage to production losses from “parent wells” Among the new technologies driv- the fracture conductivity. when an infill fracture interferes with the ing these results is an engineered stim- As the industry faces new challenges depleted well. By refracturing the deplet- ulation design software that integrates in the wake of low commodity prices and ed wells before fracturing the infill well, geological, geophysical, petrophysi- a slowdown in drilling, it is eyeing a sig- operators have successfully prevented cal, geomechanical, and microseismic nificant new opportunity to take uncon- these negative impacts and actually expe- data from the reservoir into models that Copyright 2015, Society of Petroleum Engineers. Reprinted from the Journal of Petroleum Technology with permission.76 JPT • JULY 2015 MANAGEMENT

0 0 0 Increasing Production, 15:00:00 17:00:00 19:00:00 21:00:00 23:00:00 Flow Pressures Time (hh:mm:ss) Five operators in the consortium have Fig. 1—Refracturing stages and composite pills are pumped in sequence to committed to refracturing a total of 15 promote diversion of fluid and proppant to rock bearing higher pressures and wells in the Eagle Ford, where more than production potential. Increasing treating pressure and other measurements are 400 wells are estimated to have very combined to confirm occurrence of diversion. high refracturing potential. Another 800 Eagle Ford Refracturing Consortium wells in the play are considered to have good potential. ■ Production Increase, B/D ■ % of Original Production, B1 month A recent refracturing treatment in the Eagle Ford boosted oil production 500 90 85 sevenfold, from 80 B/D to 550 B/D, bring- 76 ing the well up to 76% of the IP rate. Well- 80 head flow pressure also increased from Production Regain vs. Original Production (%)

400 line pressure of 120 psi to 5,800 psi, sug-

70 gesting the refracturing design had been effective in unlocking new, unproduced Production Increase (B/D)

56 60 resources. Post-fracture declines appear 300 48 50 to be similar or somewhat better than ini- 39 tial declines. 31 40 Modeling the long-term impact of 200 the refracturing operations using res- 30 ervoir simulation techniques indicates that a properly executed treatment on 20 a suitable well candidate can increase 100 overall production by at least 20%. This 10 improvement represents an increase in estimated ultimate recovery from 0 0 a given well, and ultimately raises the Well A Well B Well C Well D Well E Well F value of the life of maturing unconven- tional assets in North America. Eco- Fig. 2—Wells are listed in chronological order. Production gain is calculated using an average production rate 30 days before and after the refracturing. nomic models indicate rates of returns Regain is calculated with an average production rate 30 days after refracturing could exceed 30%, provided that can- as a percentage of the best monthly production during initial production. didate wells are correctly identified and

78 JPT • JULY 2015

workflows are applied to optimize the for the oil and gas industry to create a and techniques ensuring a full coverageexecution of the refracturing design new business model with a risk-sharing of the lateral stimulation, such as refrac-and treatment. mechanism that can change the eco- turing from heel to toe, to significantly As the oil and gas industry looks nomics of unconventional fields. The increase the productivity of the wells,ahead to the next decade of uncon- industry needs to continue enhancing thus lowering the total cost per barrel ofventional development, refracturing the development of those technologies oil equivalent. JPToffers significant potential for enhanc-ing recovery and optimizing field eco-nomics. New technologies combinedwith greater understanding of the sub- Sherif Foda is president of the Production Group at Schlumberger.surface are paving the way for revi- Before assuming his current role in 2013, he has held varioustalizing mature and depleted assets, management positions in Schlumberger, including president forenabling operators to increase pro- Europe & Africa; vice president and managing director for Saudiduction from existing well invento- Arabia, Kuwait, and Bahrain; vice president for Well Intervention;ries and raising the overall value of vice president for Well Services for Europe, Caspian, and Africa; andunconventional reservoirs. GeoMarket manager for Oman. Earlier in his Schlumberger career, Foda held operations management, marketing, and engineering Going forward, collaboration positions in the United Arab Emirates, Qatar, Yemen, Arabian Gulf countries, Unitedbetween service companies and opera- States, Germany, and Eastern European countries. He began his career withtors in combining geosciences, a pro- Schlumberger in 1993 in well services operations in the Red Sea in Egypt. Beforecess for identifying well candidates for joining Schlumberger, Foda worked in the information technology industry for 2 years.refracturing, and innovative technolo- Foda holds a BS degree in electronics engineering and automatic control from Aingy present a meaningful opportunity Shams University in Cairo.